Syrian opposition groups have signed a draft agreement which charts a democratic transition should president Bashar al-Assad leave office.

Violence across the country is continuing despite a visit by Arab League observers and conflicting accounts of what they have witnessed.

Representatives from the two main opposition groups, the Syrian National Council and the National Coordination Body for Democratic Change in Syria, say their draft agreement has been signed in Cairo.

Analysts say the move is a serious attempt by a fractured opposition to unite against the Syrian authorities.

The leading opposition group in exile, the SNC, signed the deal on Friday with the largely Syrian-based National Coordination Committee, according to Moulhem Droubi, a top SNC member from Syria's Muslim Brotherhood.

The two groups have received attention from Western powers, but it is not clear how much sway they hold with the mass of protesters.

A document seen by agency reporters says the deal will be presented to other opposition groups at a conference next month.

The National Coordination Committee had disagreed with the SNC's calls for foreign intervention - one of several disputes that had prevented opposition groups agreeing on what a post-Assad Syria should look like.

In their pact, the two sides "reject any military intervention that harms the sovereignty or stability of the country, though Arab intervention is not considered foreign".

The groups outlined a one-year transitional period, which could be renewed once if necessary.

In that period, Syria would adopt a new constitution "that ensures a parliamentary system for a democratic, pluralistic civil state".

The document also stresses that religious freedom will be guaranteed by the new constitution, and condemns any signs of sectarianism or "sectarian militarisation".

Most of the protesters come from Syria's Sunni Muslim majority, while Mr Assad still appears to enjoy significant support among members of his Shiite Alawite sect, from which most of the ruling establishment is drawn.

Conflicting accounts

On the ground there have been conflicting accounts of Arab League observers having seen government snipers firing on crowds in the city of Deraa and of snipers being deployed in the Damascus suburb of Douma.

In an online video a man who appeared to be a monitor in the southern town of Deraa acknowledged he had seen government snipers firing from rooftops.

"We saw snipers in the town, we saw them with our own eyes," the observer says in Arabic, visibly concerned.

"We're going to ask the government to remove them immediately. We'll be in touch with the Arab League back in Cairo."

The head of the observer mission, Mustafa Dabi, has said his colleagues were mistaken, a statement certain to confirm to demonstrators that he is biased towards the Syrian government.

Mr Dabi later told the BBC: "This man said that if he sees, by his eyes, those snipers, he will report them immediately and he will tell the government. But he didn't see."

The British-based Syrian Observatory for Human Rights said security forces had shot dead 27 people on Friday in areas where there were no observers.

The deaths add to the toll of a conflict that the United Nations says has killed more than 5,000 people, most of them unarmed civilians.